Optical recording medium and master disc for manufacturing optical recording medium

ABSTRACT

An optical recording medium allowing high-density recording, where a groove having a shallow U-shaped cross section wider than certain width, a master for manufacturing optical recording medium, a manufacturing apparatus thereof, and a manufacturing method thereof are provided. A exposure beam ( 61 ) and a exposure beam ( 62 ) are recombined together with a first exposure beam ( 60 ) in a second PBS ( 47 ) so that traveling directions thereof may be the same direction. At this time, the exposure beam ( 61 ) and the exposure beam ( 62 ) are arranged so that both optical axes may be aligned at certain distance. Thereby, a width of a spot formed by combining these beams can be extended, and light exposure of the spot can be proper to form a shallow groove, as typically showed in FIG.  3.

TECHNICAL FIELD

The present invention relates to an optical recording medium, a masterfor manufacturing optical recording medium and an apparatus and a methodfor manufacturing the master for manufacturing the optical recordingmedium.

BACKGROUND ART

As an optical recording medium, various kinds have been proposed, forexample, read-only type optical discs such as CD (compact disc) and LD(laser disc), and writable optical discs such as MO (magnetic opticaldisc) and MD (mini disc), in which a guide groove for tracking and apattern for discrete information as a pre-format are preformed.

Manufacturing methods of such various optical discs generally include astep of manufacturing a metal master called a stamper which has asurface shape corresponding to a desired concavo-convex pattern of pits,a groove, and the like (a master manufacturing step), a step of moldingfor transferring the surface shape of the stamper onto a disc substrate,and a step of forming certain layers such as a recording layer and aprotective layer.

Of these steps, in the master manufacturing step, a procedure of washingand drying a glass substrate having polished surfaces, applyingphotoresist, which is a sensitive material, on the glass substrate, andemitting the optical beams such as laser beams to the photoresist toform the pattern of the pits and the groove, is generally performed. Alatent image formed on the photoresist by the above exposure isdeveloped to form a concavo-convex pattern corresponding to thethree-dimensional pattern of the pits or the groove on the photoresist,the pattern is further transferred onto a surface of a metal by theelectroforming to produce the stamper. The procedure of recording theconcavo-convex pattern using the exposure with such optical beamsrequires faithfully transferring certain pattern onto the photoresistsurface in precision of the sub micron order.

On the other hand, a technique has been proposed for using a grooveitself as a record track in the read-only type optical discs such as CDand LD and the rewritable type discs such as MD and MO. In these opticalrecording media, while the optimal pit width and the optimal groovewidth depend on the kinds of the media, and any of the masters formanufacturing optical recording medium are manufactured by the abovemaster manufacturing methods, so the pit width and the groove width aredefined by the spot diameter of the exposure beams.

An aligner having a schematic structure as shown in FIG. 5 hasconventionally been used for recording on the optical recording medialike CD and LD using one exposure beam. The aligner comprises a gaslaser light source 101 which uses gas as an amplification medium like aHe—Cd laser, a mirror 103 which leads a laser light 102, which isemitted from the gas laser light source 101, towards a latter opticalsystem, a beam condenser 104 which condenses (reduces) the laser light102 being led through the mirror 103, an AOM (Acousto Optical Modulator)105 which modulates the optical intensity of the beam being controlledby a driver 115 corresponding to ultrasonic waves modulated and suppliedbased on record signals, a beam-diameter regulation lens 106 whichenlarges or reduces the beam diameter of the laser light 102 beingintensity-modulated by the AOM 105, a moving optical table 108, and amirror 107 which reflects the beam, which is emitted from thebeam-diameter regulation lens 106 and goes straight in a form of acollimated beam, and horizontally passes it onto the moving opticaltable 108.

Furthermore, on the moving optical table 108 are arranged a third lens109, a mirror 110, and an objective lens 111. The third lens 109 isarranged in a position which makes the beam of the laser light 102gather on an incident side condensing surface 113 which is formed in aposition conjugated with an imaging condensing surface 112 of theobjective lens 111. An exposure beam is directed to a photoresist film114 via the third lens 109 of the moving optical table 108, the mirror110, and the objective lens 111.

In addition, the spot diameter of the exposure beam can be adjusted bychanging a focal distance of the beam-diameter regulation lens 106 orthe third lens 109 being positioned between the gas laser light source101 and the objective lens 111, and further readjusting an effectivenumerical aperture NA of the objective lens 111 so that the objectivelens 111 may condense the exposure beam on a surface of the photoresistfilm 114.

On the other hand, for example, in the MO discs, the technology ofrecording pits and a groove with two exposure beams has been proposed,for example, in Japanese Laid Open No. 06-103613. As shown in FIG. 6, inan optical recording apparatus, on the same optical axis are arrangedone laser light source 201, a beam splitter 203 which divides a beam oflaser light 202 being emitted from the laser light source 201 into twobeams, a reflective mirror 204, a beam relay optical system 205, a beamrelay optical system 206, and a moving optical table 208 equipped with aPBS (polarization beam splitter) 207 which regenerates the two dividedlaser beams.

The laser light 202 being emitted from the laser light source 201, goesstraight keeping a form of a collimated beam, and is divided intoreflected light (S polarized light) 209 and passing light (S polarizedlight) 210 by the beam splitter 203. The passing light 210 is reflectedfrom the reflective mirror 204 and directed onto the beam relay opticalsystem 206, and the reflected light 209 is directly led to the beamrelay optical system 205. The passing light 210 is condensed on a firstAOM 212 with a condenser lens 211 within the beam relay optical system206. The first AOM 212 is controlled by a driver 214 and modulates theintensity of the beam of the passing light 210. The beam which is,intensity-modulated by the first AOM 212 is reflected from a lens 213 tobecome a collimated beam of P polarized light. The collimated beam ispolarized by a λ/2 polarizing plate 215 to become a collimated beam 216of S polarized light.

On the other hand, the reflected light 209 becomes a collimated beam 221of S polarized light through the beam relay optical system 205comprising a condenser lens 217, a driver 218, a second AOM 219, and alens 220.

The collimated beam 216 is reflected from a mirror 222, the collimatedbeam 221 is reflected from a mirror 223, and both are horizontallydirected to the moving optical table 208 in parallel. In the movingoptical table 208, the collimated beam 216 passes directly through thePBS 207. On the other hand, the collimated beam 221 is reflected from amirror 224 to shift the traveling direction 90 degrees away from theoriginal direction to be directed to the PBS 207, reflected inside thePBS 207, and aligned on the optical axis of an objective lens 226through a lens 225 and a reflective mirror 227. As described above, thetwo collimated beams 216 and 221 which enter the PBS 207 are combinedwith the PBS 207. Here, a reflective surface of the PBS 207 is set sothat the traveling direction of the combined and emitted laser beams mayhave a moderate angle of reflection. Thus, when the laser beams beingemitted from the PBS 207 are condensed on a surface of a photoresistfilm 228 which is an exposed object and is parallel to an imagingcondensing surface of the objective lens 226, spots of the twocollimated beams 216 and 221 can be condensed respectively in positionswhich are shifted on the order of sensitivity and resolution of thephotoresist film 228 and pits are exposed in the nearly center betweenadjacent parts of the groove in the radius direction.

Using such exposure method, a latent image of pits and a groove based onMO formats can be exposed (recorded). Furthermore, a latent image ofpits and a groove based on various formats such as single density MO,double density MO, and quad density MO can be exposed (recorded) bychanging focal distances of the condenser lenses 211 and 217 and thelens 225, readjusting so that the objective lens 226 may condense beamson the surface of the photoresist film 228, and changing the diameter ofthe spots of the exposure beams.

Incidentally, it is confirmed that there is possibility that pits withan U-shaped cross section and wobbling grooves shallower than the depthof the pits may become a leading technology corresponding to increasedhigh density for realizing increasing the storage capacity thereof inoptical recording media such as DVD-RW (digital versatiledisc-rewritable) upon which practice of high density recording isimposed. DVD are generally set to perform recording on flat parts whichcan secure predetermined amounts of record signals, for example, on thebottoms of the grooves and on the upper surfaces of lands, and it isconfirmed that effective recording and reproduction of information arepossible, even if recording parts are located in a comparatively shallowposition.

When such master for manufacturing optical recording medium is produced,pits 301 are exposed so that espousing light for a photoresist film 302may be deep enough to reach even a surface of a substrate 303 astypically shown in FIG. 7, so the cross section thereof has a U-shapeddeep hole with a flat bottom 304.

However, in order to form a groove 305 shallower than the pits 301,light exposure for exposing the photoresist film 302 is purposelyreduced to stop the exposing at a shallow place on the way withoutextending to a deep position in the thickness direction of thephotoresist film 302 during producing the master for manufacturingoptical recording medium, but a three-dimensional pattern of theshallower groove 305 obtained by developing a latent image formed withsuch lowered exposure light has a cross section of a V-shaped groove,and the width Wg of the groove 305 (the width in the radius direction ofthe disc-like substrate 303) narrows down to half or less of the widthWp of the pits 301, which results in a problem that sufficient amountsof servo signals (amounts of PUSH-PULL signals) at the time ofreproduction or the like of the optical recording media manufacturedfrom such master can not be obtained. Moreover, the V-shaped crosssection of the groove 305 increases deviation (dispersion) ofdistribution of the depth dg of the groove, which results in a problemthat recording and reproduction properties are lowered. Moreover, in themanufacturing process of the optical recording medium, laminating andforming furthermore a reflective film, a protective layer, and the likeon a surface of the shallow groove with the V-shaped cross section canfurther reduce the substantial width of the groove 305.

And, in order to solve these problems, it is considered that there isalso a method of increasing the light exposure to obtain certain widthin the step of exposing the shallow groove 305 which is the factorthereof, but such increase of light exposure makes the exposure reach adeep position in the thickness direction of the photoresist film 302,and it is significantly difficult to form the groove 305 having theU-shaped cross section with certain width and shallower than the pits301 in the conventional technique, for example, it is impossible to formeven the groove 305 shallower than the pits 301.

The present invention has been achieved in view of the above problems.It is an object of the invention to provide an optical recording mediumenabling high density recording, where a groove having U-shaped crosssection being shallower than pits and the like and being wider thancertain width is formed, a master for manufacturing optical recordingmedium, a manufacturing apparatus for manufacturing the master and amanufacturing method thereof.

DISCLOSURE OF THE INVENTION

An optical recording medium according to the present invention has agroove and plural pits formed and arranged dispersedly in acircumference direction, which are formed on a substrate with a shapesuch as a disc shape or a polygon, and the groove is formed to have aU-shaped cross section which is shallower than a depth of the pits.

A master for manufacturing optical recording medium according to thepresent invention where a groove and plural pits formed and arrangeddispersedly in a circumference direction, are formed on a substrate,wherein the groove of the optical recording medium is formed to have aU-shaped cross section which is shallower than a depth of the pits.

An apparatus for manufacturing a master for manufacturing opticalrecording medium according to the present invention where a groove andplural pits formed and arranged dispersedly in a circumferencedirection, are formed on a substrate, comprises: a first beam splitterfor dividing single exposure beam supplied from a light source into twobeams; a pit modulation means for form the pit-modulating one beam ofthe divided beams; a pit exposure means for forming a latent image forforming the pits by irradiating a surface of the master with thepit-modulated beam; a wobble deflecting means for optically deflectingthe other beam of the divided beams for wobbling; a second beam splitterfor dividing the beam, which is optically deflected for wobbling, intoplural exposure beams; and a groove exposure means for forming a latentimage for forming a groove with an U-shaped cross section and shallowerthan a depth of the pits on the surface of the master by arranging theplural exposure beams to be aligned at certain widths in the radiusdirection of the master with a polarization beam splitter andirradiating an exposure beam with a spot wider in the radius directionof the master than that of the above single exposure beam to the surfaceof the master.

Moreover, another apparatus for manufacturing a master for manufacturingoptical recording medium according to the present invention having atleast a groove on a substrate, comprises: a wobble deflecting means foroptically deflecting single exposure beam supplied from a light sourcefor wobbling; a beam splitter for dividing the deflected beam intoplural exposure beams; and a groove exposure means for forming a latentimage for forming a groove with an U-shaped cross section on a surfaceof the master by arranging the plural exposure beams to be aligned atcertain widths in the radius direction of the master with a polarizationbeam splitter, and irradiating an exposure beam with a spot wider in theradius direction of the master than that of the above single exposurebeam to the surface of the master.

A method of manufacturing a master for manufacturing optical recordingmedium according to the present invention where a groove and plural pitsformed and arranged dispersedly in a circumference direction, are formedon a substrate, wherein a single exposure beam supplied from a lightsource is divided into two beams with a first beam splitter, one beam ofthe divided beams is pit-modulated and irradiated to a surface of themaster to form a latent image for forming the pits, the other beam ofthe divided beams is optically deflected for wobbling, and divided intoplural exposure beams with a second beam splitter, and the pluralexposure beams are arranged to be aligned at certain widths in theradius direction of the master with a polarization beam splitter and anexposure beam with a spot wider in the radius direction of the masterthan that of the above single exposure beam is irradiated to the surfaceof the master in order to form a latent image for forming a groove withan U-shaped cross section on the surface of the master.

Moreover, another method for manufacturing a master for manufacturingoptical recording medium according to the present invention having atleast a groove on a substrate, wherein a single exposure beam suppliedfrom a light source is optically deflected for wobbling and divided intoplural exposure beams with a beam splitter, the plural exposure beamsare arranged to be aligned at certain widths in the radius direction ofthe master with a polarization beam splitter, and an exposure beam witha spot wider in the radius direction of the master than that of theabove single exposure beam is irradiated to a surface of the master inorder to form a latent image for forming a groove with an U-shaped crosssection on the surface of the master.

In an optical recording medium, a master for manufacturing opticalrecording medium, and an apparatus and method for manufacturing a masterfor manufacturing optical recording medium according to the presentinvention, a latent image for forming a groove with an U-shaped crosssection is formed on the master for manufacturing optical recordingmedium by optically deflecting for wobbling on single exposure beamsupplied from the light source, dividing the optically deflected beaminto the plural exposure beams, arranging the plural exposure beams tobe aligned at certain widths in the radius direction of the master, andirradiating the exposure beam with a spot wider in the radius directionof the master than that of the above single exposure beam to the master.The latent image is developed to obtain the master for manufacturingoptical recording medium having an original form of the groove with theU-shaped cross section. And the optical recording medium having thegroove where the depth is shallower than the depth of the pits and thecross section thereof is formed to be U-shaped is manufactured using themaster.

In addition, the shape of the cross section of the above groove ispreferably to be the U-shaped groove with a ratio of a bottom width toan aperture width in set to 17% or more. It should be noticed that theratio of the bottom width to the aperture width of the U-shaped grooveis not limited only to this, but may be set to less than 17% dependingon formats of optical recording media.

Moreover, if λ is defined as wavelength of light for reproducing(reading) or for recording (writing), it is desirable to set the depthof the pits to λ/4 and to set the depth of the groove to λ/8, and thisis not to say that it is not limited only to these.

A groove obtained by irradiation of one exposure beam in theconventional case has a bottom which is substantially not flat and aV-shaped or V shaped valley-like cross section. In any case, accordingto the optical recording medium of the present invention, the crosssection form of the groove can be the U-shape, and the bottom of thegroove can substantially be flat by arranging the plural exposure beamsto be aligned at certain widths in the radius direction of the master,and irradiating the exposure beam with a spot wider in the radiusdirection of the master than that of the above single exposure beam tothe master, as described above. The width of the flat bottom can be setand changed to various values, for example, 17% or more to the aperturewidth as described above, by adjusting intervals among center axes ofthe plural exposure beams. Moreover, the number of the beams arranged inthe radius direction of the master can be set to two, three, or muchmore if needed.

Other and further objects, features and advantages of the invention willappear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing a schematic structure of an optical recordingapparatus used in a step of manufacturing a master of an opticalrecording medium according to a first embodiment of the invention.

FIG. 2 is a view showing a schematic structure of an optical recordingapparatus used in a step of manufacturing a master according to a secondembodiment of the invention.

FIG. 3 is a view typically showing a glass master for manufacturingoptical recording medium produced by the optical recording apparatusaccording to the first embodiment.

FIG. 4 is a view typically showing a glass master produced by theoptical recording apparatus according to the second embodiment.

FIG. 5 is a view showing a schematic structure of a conventional alignerfor recording a pattern of pits and the like of an optical recordingmedium such as CD or LD with single exposure beam.

FIG. 6 is a view showing a schematic structure of a conventional alignerfor recording pits and a groove with two exposure beams.

FIG. 7 is a view typically showing a glass master manufactured by aconventional technique.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described in detail belowwith reference to accompanying drawings.

First Embodiment

FIG. 1 is a view showing a schematic structure of an optical recordingapparatus (a manufacturing apparatus for a master for manufacturingoptical recording medium) used in steps of manufacturing a master formanufacturing optical recording medium according to a first embodimentof the invention. It should be noticed that, in an optical recordingmedium according to the embodiment, a main concavo-convex pattern isformed on the surface thereof, using the master produced by the opticalrecording apparatus, and principal parts of a method for manufacturingthe master according to the embodiment is embodied by operations of theoptical recording apparatus, so these will be also explainedhereinafter.

The optical recording apparatus is used for forming a so-called stamper(a master for manufacturing optical recording medium) for transferring adesired concavo-convex pattern on a surface of a disc substrate in anoptical disc manufacturing process, divides a laser beam 13 emitted froma laser light source 1 into two beams of a first exposure beam (acollimated beam 16) for exposing a pattern of pits and a second exposurebeam (a collimated beam 17) for exposing a pattern of a wobbled groove(a wobbling groove) with a beam splitter 5, divides furthermore thesecond exposure beam into two exposure beams 61 and 62, arranges them atcertain widths (intervals) in a radius direction of a round-plate-shapedmaster for manufacturing optical recording medium, irradiates aphotoresist film 12 of the master for manufacturing optical recordingmedium with an exposure beam 10 with a wider spot extended in the radiusdirection, and forms a latent image to obtain the shallower wobblinggroove with a U-shaped cross section after developing.

The optical recording apparatus comprises the laser light source 1, afirst modulation optical system (it is called a first OM hereinafter) 2,a second modulation optical system (it is called a second OMhereinafter) 3, a moving optical table 4, and a λ/2 polarizing plate 9as a principal part. Furthermore, on an optical axis through them, itcomprises the beam splitter 5 and mirrors 6, 7, and 8 in order to leadthe laser beam 13, and the exposure beam 10 may be set to be directedfinally to the photoresist film 12 on a glass substrate 11 of themaster.

As the laser light source 1, an apparatus for oscillating laser lightfor recording like a Kr laser (λ=351 nm) can suitably be used, forexample. This is not to say that the laser light source 1 cannot belimited particularly to this and other apparatuses may suitably beselected and used.

The laser beam 13 emitted from the laser light source 1 goes straightkeeping a form of a collimated beam, and is divided into reflected light(a beam 14) and passing light (a beam 15) by the beam splitter 5. Thebeam 14 reflected from the beam splitter 5 is directed on to the secondOM 3. On the other hand, the beam 15 passing through the beam splitter 5is reflected from a surface of the mirror 6 and is directed on to thefirst OM 2.

In the first OM 2, the beam 15 is condensed on a first AOM (AcoustoOptical Modulator) 21 by a condenser lens 22. Laser light emittedtherefrom which is intensity modulated by the first AOM 21 becomes thecollimated beam 16 through a lens 23.

On the other hand, in the second OM 3, the beam 14 is condensed on asecond AOM 31 by a condenser lens 32, and emitted laser light which isintensity modulated by the second AOM 31 becomes the collimated beam 17through a lens 33.

The collimated beam 16 emitted from the first OM 2 is reflected from themirror 7, becomes P polarized light through the λ/2 polarizing plate 9,and is horizontally directed to the moving optical table 4 in parallel.The collimated beam 17 emitted from the second OM3 is reflected from themirror 8 and is horizontally directed to the moving optical table 4 inparallel.

The moving optical table 4 comprises a first PBS (polarization beamsplitter) 41, an AOD (Acousto Optical Deflector) 42, wedge prisms 43 and44, a beam splitter 45, mirrors 46 and 50, a second PBS 47, a λ/2polarizing plate 48, a lens 49, and an objective lens 51 as a principalpart. In addition, the AOD 42 is set to be driven and controlled by aVCO (Voltage Controlled Oscillator) 53 and a driver 52 based on timingsignals of 140.7 kHz supplied from an external.

The collimated beam 16, which is emitted from the first OM 2 and led toreach the moving optical table 4, passes through the first PBS 41, theλ/2 polarizing plate 48 and the lens 49, is reflected from the mirror50, is condensed on the objective lens 51, and is directed to thephotoresist film 12 as the exposure beam to form the latent image of thepits.

On the other hand, the collimated beam 17 which is emitted from thesecond OM 3, after reaching the moving optical table 4, is opticallydeflected by the AOD 42, is reflected from the beam splitter 45 to bendthe traveling direction by 90 degrees, and enters the first PBS 41.Moreover, the collimated beam 17, after passing through the beamsplitter 45, is reflected from the mirror 46 to bend the travelingdirection by 90 degrees, and enters the second PBS 47.

Incidentally, the AOD 42 performs the optical deflection on thecollimated beam 17 so that the groove may be wobbled to become awobbling groove. That is, the collimated beam 17 which is emitted fromthe second OM 3 and directed to enter the AOD 42, enters the AOD 42through the wedge prism 43, and is optically deflected by the AOD 42 inorder to correspond to the exposure pattern. As acousto optical elementsused for the AOD 42, a material made of tellurium oxide (TeO₂) ispreferable, for example. The collimated beam 17 is emitted through thewedge prism 44 after the optical deflection thereof by the AOD 42. Thesewedge prisms 43 and 44 are set so that the collimated beam 17 may entera lattice surface as the acousto optical elements of the AOD 42satisfying the Bragg condition. Furthermore, they are also set not tochange the horizontal height of the collimated beam 17, even when theAOD 42 performs the optical deflection on the collimated beam 17. Inother words, the wedge prism 43, the AOD 42, and the wedge prism 44 arelocated so that the lattice surface of the acousto optical elements ofthe AOD 42 being subject to the collimated beam 17 satisfies the Braggcondition and that the horizontal height of the collimated beam 17emitted from the AOD 42 may be not changed.

The AOD 42 is controlled by a driver 52. High frequency signals from aVCO 53 are supplied to the driver 52 with sin wave control signals. Atthe time of exposing a desired pattern, signals corresponding to thepattern are inputted from the VCO 53 into the driver 52, the AOD 42 isdriven by the driver 52 based on the signals to perform the opticaldeflection on the collimated beam 17.

In detail, in the case of wobbling a groove with a frequency of 140.7kHz in order to add address information on the groove, for example,signals which is obtained by phase modulation of high frequency signalswith a center frequency of 224 MHz using control signals with afrequency of 140.7 kHz are supplied from the VCO 53 to the driver 52.Based on these signals, the driver 52 drives the AOD 42, the Bragg angleof the acousto optical elements of the AOD 42 is changed, and thereby,the optical deflection is performed on the collimated beam 17corresponding to the wobbling with a frequency of 140.7 kHz.

The collimated beam 17, which is optically deflected by the AOD 42 tocorrespond to the wobbling of the wobbling groove in such a way, isreflected from the beam splitter 45 to bend the traveling direction by90 degrees, and enters the first PBS 41 (the beam emitted therefrom iscalled a 2-1 exposure beam 61 for convenience, hereinafter), asdescribed above. Moreover, the collimated beam 17 passing through thebeam splitter 45 is reflected from the mirror 46 to bend the travelingdirection at 90 degrees and enters the second PBS 47 (the beam emittedtherefrom is called a 2-2 exposure beam 62 hereinafter).

The 2-1 exposure beam 61 is reflected from the first PBS 41 and passesthrough the λ/2 polarizing plate 48 and the second PBS 47. The 2-2exposure beam 62 is reflected from the second PBS 47. And the 2-1exposure beam 61 and the 2-2 exposure beam 62 are recombined with thecollimated beam 16 in the second PBS 47 to have the same travelingdirection. At this time, the 2-1 exposure beam 61 and the 2-2 exposurebeam 62 are arranged so that both optical axes thereof may be aligned atcertain distance. As typically showed in the FIG. 3, the width of thespots formed by combining those beams can be extended, the lightexposure of the beams can be adjusted to form shallow grooves.Consequently, the master, which has a wobbling groove three-dimensionalpattern 80 for forming the wobbling groove with a shallow U-shaped crosssection and a three-dimensional pattern 90 of pits, can be manufactured,and furthermore, the optical recording medium having the wobbling groovewith the shallow U-shaped cross section can be manufactured using themaster.

In addition, the collimated beam 16 is for exposing the pattern 90 ofthe pits after being emitted from the second PBS 47, so the beam at thesecond PBS 47 and forward is called an first exposure beam 60. The spotof the first exposure beam 60 for exposing the pits, after beingrecombined as described above, is arranged so that the optical axisthereof may be aligned at certain distance from the spot for thewobbling groove, as a distinct spot from the spot for the wobblinggroove formed by combining the 2-1 exposure beam 61 and the 2-2 exposurebeam 62.

The recombined 2-1 exposure beam 61 and 2-2 exposure beam 62 passthrough the lens 49, which is a magnifying lens, to have certain beamdiameters respectively, are reflected from the mirror 50 to be led tothe objective lens 51, and are directed onto the photoresist film 12through the objective lens 51. Thereby, the photoresist film 12 isexposed and the latent image is formed. At this time, the glasssubstrate 11 on which the photoresist film 12 is applied is driven byrotation drive using a rotation driving apparatus (not shown) asindicated by an arrow M in the figure so that the desired patterns 80and 90 may be exposed on the whole surface of the photoresist film 12,and the position from the moving optical table 4 is relatively shiftedin parallel. In such way, the latent image corresponding to irradiationtracings of the first exposure beam 60, the 2-1 exposure beam 61 and the2-2 exposure beam 62, is formed on the almost whole surface of apredetermined recording range of the photoresist film 12. Afterdeveloping the latent image, the optical recording medium based on theformat, which is the suitable format for DVD-RW or the like and canrealize high density recording, of the pits and the wobbling grooveshallower than the pits and the U-shaped cross section, can be realized.

Here, the first PBS 41 and the second PBS 47 are set to reflect Spolarized light and transmit P polarized light. Moreover, the collimatedbeam 16 emitted from the first OM 2 passes through the λ/2 polarizingplate 9 to rotate the polarizing direction by 90 degrees and become Ppolarized light, and further, the λ/2 polarizing plate 48 rotates thepolarizing direction thereof to obtain P polarized light.

The collimated beam 17 which is optically deflected for wobbling by theAOD 42 is divided into the 2-1 exposure beam 61 and the 2-2 exposurebeam 62 by the beam splitter 45 as described above, and they arerecombined with the second PBS 47 so that the optical axes thereof maybe aligned at certain intervals in parallel each other.

The 2-1 exposure beam 61 is S polarized light, and is reflected from thefirst PBS 41, the polarizing direction is optically rotated by the λ/2polarizing plate 48, and a P polarized light component passestherethrough and enters the second PBS 47. Moreover, the 2-2 exposurebeam 62 is S polarized light and is reflected from the second PBS 47,and at this time, is recombined to be in parallel with the 2-1 exposurebeam 61 in the direction of the optical axis.

The 2-1 exposure beam 61 and the 2-2 exposure beam 62 which arerecombined with the direction of the optical axis can be arranged on thephotoresist film 12 so that the optical axes thereof may be aligned atthe certain intervals in the radius direction by changing the angle ofthe second PBS 47, and the transmitted light of the 2-1 exposure beam 61can be adjusted by rotation adjustment of the λ/2 polarizing plate 48 toequalize the beam intensity.

In addition, for example, a numerical aperture NA of the objective lens51 is preferably set to 0.9 in an example such as the above setting.Moreover, control signals from an input terminal which is not shown aresupplied to the first AOM 21 and the second AOM 31. In the first AOM 21for forming the pits, the control signals are EFM+(8-16 modulation)signals, and the laser light is intensity modulated (ON/OFF) by theEFM+signals. Moreover, in the second AOM 31 for forming the groove, DCsignals with a fixed level are used.

Second Embodiment

A second embodiment is obtained by furthermore changing the opticalrecording apparatus and the manufacturing method comprising the mainstep of exposing the master in the above first embodiment, where thecollimated beam 17 which is the second exposure beam for exposing thepattern 80 of the wobbling groove is divided into three exposure beams(they are called the 2-1 exposure beam 61, the 2-2 exposure beam 62, anda 2-3 exposure beam 63) using beam splitters 45 and 71 and the mirror46, and they are combined so that optical axes thereof may be aligned atcertain intervals in the radius direction. Thereby, a spot width of anexposure beam 70 for finally directing to a photoresist and exposing awobbling groove is extended, and a latent image of the shallow U-shapedwobbling groove is formed.

FIG. 2 is a view showing a schematic structure of an optical recordingapparatus used in a step of manufacturing a master of an opticalrecording medium according to the second embodiment of the invention. InFIG. 2, in order to intend simplification of illustration andexplanation thereof, the same parts as those indicated in FIG. 1 aredenoted by the same symbol.

In the optical recording apparatus according to the second embodiment,the collimated beam 17 which is optically deflected by the AOD 42 forwobbling is divided into three beams of the 2-1 exposure beam 61, the2-2 exposure beam 62, and the 2-3 exposure beam 63 by the beam splitter45 and the beam splitter 71. The 2-1 exposure beam 61, the 2-2 exposurebeam 62, and the 2-3 exposure beam 63 are recombined with the second PBS47 and a third PBS 72 so that the optical axes thereof may be aligned atthe certain intervals in the radius direction of the master, whichresults in forming the exposure beam having the wider spot and loweredlight exposure in order to form the latent image of thethree-dimensional pattern 80 of the shallow wobbling groove having aU-shaped cross section and a wider bottom as typically shown in FIG. 4,on the photoresist film 12.

The 2-1 exposure beam 61, which is the S polarized light, is reflectedfrom the first PBS 41, is changed into P polarized light by rotating(optically rotating) the polarizing direction with the λ/2 polarizingplate 48, and passes therethrough, and the 2-2 exposure beam 62 and the2-3 exposure beam 63, which are S polarized light, are reflectedrespectively from the second PBS 47 and the third PBS 72, and arerecombined with the third PBS 72. A width of a spot formed by therecombination of the 2-1 exposure beam 61, the 2-2 exposure beam 62 andthe 2-3 exposure beam 63 for irradiating the photoresist film 12, can beadjusted by changing the angles of the second PBS 47 and the third PBS72. Moreover, the beam intensity can be equalized by adjusting therotation of the λ/2 polarizing plate 48 to adjust transmitted light ofthe 2-1 exposure beam 61 through the first PBS 41 and the second PBS 47.

In such a way, the optical recording medium having the pits and thewobbling groove with the shallow U-shaped cross section, and the widebottom, which is an optical recording medium based on a suitable formatfor DVD-RW or the like, can be realized. If requirements, for example,various exposure conditions such as wavelength of the laser beams andsensitization properties of the photoresist, and the depth on thewobbling groove, are the same as the case where the latent image of thewobbling groove is exposed by the combination of the two exposure beamsas shown in the first embodiment, arranging and aligning the threeexposure beams like the second embodiment or more exposure beams canprovide the wobbling groove with the wider bottom compared with theabove case, and also improve further the flatness of the bottom.

[Example of the Method of Manufacturing the Optical Disc]

Based on the method of manufacturing the optical disc as described inthe above second embodiment, a master was actually manufactured andfurther an optical disc was manufactured using the master.

First, in the step of manufacturing the master, a master formanufacturing optical recording medium which has a three-dimensionalpattern 80 corresponding to pits and a shallow U-shaped wobbling groovewas produced using the optical recording apparatus according to thesecond embodiment.

In the step of manufacturing the master, first, a disc-like glasssubstrate 11 with polished surfaces was cleaned and dried, and then, aphotoresist film 12 which was a sensitive material was applied on theglass substrate 11. The photoresist film 12 was exposed by the opticalrecording apparatus, and a latent image of the pits and the shallowU-shaped wobbling groove was formed on the photoresist film 12.

A Kr laser light source which emits laser light at a wavelength λ of 351nm was used as the laser light source 1. A lens with a numericalaperture NA of 0.9 was used as the objective lens 51 for condensing thefirst exposure beam 60, the 2-1 exposure beam 61, the 2-2 exposure beam62, and the 2-3 exposure beam 63 on the photoresist film 12. Moreover, alens with a focal distance of 80 mm was used as the lens 49 for beamexpansion.

When the photoresist film 12 is exposed using a laser cutting apparatus,the latent image of the deeper pits is formed on the photoresist film 12by exposing the photoresist film 12 to the first exposure beam 60, andthe latent image of the shallow U-shaped wobbling groove is formed onthe photoresist film 12 by exposing the photoresist film 12 to the 2-1exposure beam 61, the 2-2 exposure beam 62, and the 2-3 exposure beam63. In addition, when the photoresist film 12 is exposed to form thelatent image of the pits and the wobbling groove, the glass substrate 11on which the photoresist film 12 is applied, is driven and rotated atcertain rotation speed, and the moving optical table 4 is movedrelatively in parallel with the photoresist film 12 at certain rate.

Specifically, the rotation speed of the glass substrate 11 was set sothat a relative movement speed of the light spot of the first exposurebeam 60 and the photoresist film 12 may become a linear velocity of 3.49m/s, the moving optical table 4 was set to move relatively in the radiusdirection thereof in parallel with the glass substrate 11 by 0.74 μm(namely, one track pitch length) for every rotation of the glasssubstrate 11.

The optical intensity modulation by the second OM 3 and the opticaldeflection by the AOD 42 as described in the second embodiment isperformed on the 2-2 exposure beam 62, when exposing the photoresistfilm 12 to the 2-2 exposure beam 62 to form the latent image of thewobbling groove having the shallow U-shaped cross section on thephotoresist film 12. Here, the shallow U-shaped wobbling groove iscontinuous with certain depth, so the optical intensity modulation bythe second OM 3 is continued so that the optical intensity of thecollimated beam 17 may become constant during forming the latent imagecorresponding to the shallow U-shaped wobbling groove.

Then, the optical deflection was performed on the collimated beam 17 bythe AOD 42. Specifically, in order to perform the optical deflection onthe collimated beam 17, control signals, which are obtained bymodulating high frequency signals based on timing control signals, aresupplied from the VCO 53, which is the voltage controlled oscillator, tothe driver 52, and the driver 52 drives the AOD 42 based on the controlsignals to change the Bragg angle as the acousto optical elements. Inthe example, the optical deflection was performed as follows: FMmodulation was performed on high frequency signals having a centerfrequency of 224 MHz based on timing control signals having a frequencyof 140.7 kHz to obtain the control signals; and, the driver 52 wascontrolled and driven by the VCO 53 based on the control signals, sothat a combined spot of the exposure beam 70 condensed on thephotoresist film 12 oscillated at a frequency of 140.7 kHz at ±10 nmoscillations in the radius direction of the glass substrate 11, and flattracking of the pattern 80 of the groove exposed on the photoresist film12 was wobbled.

The collimated beam 17, which is intensity modulated and opticallydeflected in such a way, is once divided into the three beams of the 2-1exposure beam 61, the 2-2 exposure beam 62, and the 2-3 exposure beam 63by the beam splitter 45 and the beam splitter 71, and further, thesethree beams were recombined with the second PBS 47 and the third PBS 72so that their optical axes may be aligned at certain intervals in theradius direction of the glass substrate 11. The exposure beam 70obtained by the recombination passes through the lens 49 to adjust thespot diameter, is reflected from the mirror 50 to change the travelingdirection by 90 degrees, and is condensed on the photoresist film 12 bythe objective lens 51. Thereby, the latent image corresponding to thewobbling groove with the shallow U-shaped cross section was formed onthe photoresist film 12.

For exposing the photoresist film 12, the glass substrate 11 on whichthe photoresist film 12 was applied, was driven and rotated at certainrotation speed and moved in parallel at certain speed as described inthe above embodiment. Specifically, the rotation speed of the glasssubstrate 11 was set so that the relative movement speed of the exposurebeam 70 (in other words, of the moving optical table 4) and thephotoresist film 12 may be a linear velocity of 3.49 m/s. Moreover, themoving optical table 4 was moved in parallel in the radius direction ofthe glass substrate 11 by every 0.74 μm corresponding to one track pitchfor every rotation of the glass substrate 11.

In addition, the power of the first exposure beam 60 for recording thepits when exposing the photoresist film 12 was 2.0 mW, and the power ofthe collimated beam 17 which is the second exposure beam for recordingthe shallow U-shaped wobbling groove was 2.0 mW for using the two beamsof the 2-1 exposure beam 61 and the 2-2 exposure beam 62 beams, or was3.0 mW for using a total of three beams of the 2-1 exposure beam 61, the2-2 exposure beam 62, and the 2-3 exposure beam 63. The setting in sucha way can suitably adjust the desired width of the wobbling groove withthe shallow U-shaped cross section, and adjusting the power of theexposure beams can reduce the depth thereof to be as shallow as halfdepth of the pits. However, the depth is not limited only to this but itis possible to be adjusted to a desired depth by variously changing thesettings of the power of the exposure beams.

After forming the latent image on the photoresist film 12 in such a way,the glass substrate 11 was located on a turntable of a developmentmachine (not shown) so that the surface on which the photoresist film 12is applied may face up. And rotating the glass substrate 11 togetherwith the turntable, a developer was dropped on the photoresist film 12to perform the development, which formed the concavo-convex patterncorresponding to the deep pits and the wobbling groove having theshallow U-shaped cross section on the glass substrate 11.

Next, a conductive film made of nickel or the like was formed on theconcavo-convex pattern by the electroless plating, and after that, theglass substrate 11 having the conductive film thereon was mounted in anelectrocasting apparatus and a plating layer with a thickness of about300±5 μm made of nickel or the like was formed on the conductive film bythe electroplating process. Then, the plating layer was peeled, thepeeled plating was cleaned using acetone or the like to remove thephotoresist film 12 remaining on the concavo-convex pattern transferredsurface.

This accomplished the master for manufacturing optical recording mediumcomposed of the plating on which the concavo-convex pattern formed onthe glass substrate 11 was transferred, i.e., the master on which theconcavo-convex pattern corresponding to the deep pits and the shallowU-shaped wobbling groove. The master for manufacturing optical recordingmedium is used for manufacturing the optical disc where the wobblinggroove with the shallow U-shaped cross section is formed to have aspiral shape along a recording track.

Next, a disc substrate on which the concavo-convex pattern of thesurface of the above master was transferred was produced by thephotopolymerization process (the so-called 2P process) as a transferstep.

Specifically, first, a photopolymer was smoothly applied on the surfaceon which the concavo-convex pattern of the master was formed, in orderto form a photopolymer layer, and then a base plate was adhered thereonpreventing bubbles and garbage from entering the photopolymer layer. Asthe base plate, a base plate made of polymethylmethacrylate (refractiveindex thereof is 1.49) with a thickness of 0.6 mm was used.

Then, the photopolymer was hardened by ultraviolet irradiation, andfurthermore the master was peeled from the photopolymer layer to obtainthe disc substrate on which the shape of the surface of the master wastransferred.

This is not to say that the disc substrate can be produced by theinjection molding using a transparent resin such aspolymethylmethacrylate or polycarbonate for mass producing the discsubstrates, while the disc substrate was here produced using the 2Pprocess to surely transfer the concavo-convex pattern which is formed onthe master.

Next, as a deposition step, a recording layer and a protective layerwere formed on the disc substrate on which the surface shape of themaster was transferred. Specifically, first, a first dielectric filmmade of SiN or the like, a phase-change recording film made of a GeSbTealloy or the like and a second dielectric film made of SiN or the likewas sequentially formed on the concavo-convex pattern formed surface ofthe disc substrate by the sputtering, and furthermore a light reflectingfilm made of Al alloy or the like was formed on the second dielectricfilm, in order to form the recording layer composed of the firstdielectric film, the phase-change recording film, the second dielectricfilm, and the light reflecting film for example. Then, the protectivelayer was formed by applying an ultraviolet curing resin on therecording layer by the spin coat process, and irradiating theultraviolet curing resin with ultraviolet rays to cure the resin. Thisaccomplished the phase-change optical disc.

[Evaluation of the Manufactured Optical Disc]

Stampers, which are actually manufactured like the above example usingthe method of manufacturing the master as described in the firstembodiment and the second embodiment, were measured using an AFM (AtomicForce Microscope) in the terms of a width and a depth of pits, and anaperture width, a bottom width, and a groove depth of a shallow U-shapedwobbling groove.

A stamper A was obtained by exposing a pattern 80 of a wobbling groovewith the exposure beam 10 composed of the recombined two beams of the2-1 exposure beam 61 and the 2-2 exposure beam 62, using the methoddescribed in the first embodiment. The results of measuring the stamperA were that the pits had a depth of 80 nm, an aperture width (upperwidth) of 320 nm and a bottom width (lower width) of 210 nm, and thatthe wobbling groove had an aperture width of 390 nm and a bottom widthof 150 nm, and groove depths toward the bottom of 21 nm, 31 nm, and 42nm by adjusting the power of the exposure beam 10.

A stamper B was obtained by exposing a wobbling groove with the exposurebeam 70 composed of the recombined three beams of the 2-1 exposure beam61, the 2-2 exposure beam 62, and the 2-3 exposure beam 63, using themethod described in the second embodiment. The results of measuring thestamper B were that pits had a depth of 81 nm, an aperture width (upperwidth) of 320 nm and a bottom width (lower width) of 200 nm, and thatthe wobbling groove had an aperture width of 520 nm and a bottom widthof 280 nm, and groove depths toward the bottom of 19 nm, 29 nm, and 39nm by adjusting the power of the exposure beam 70.

Next, an optical disc A and optical disc B for evaluation were producedrespectively using the stamper A and the stamper B as described above,and the evaluation thereof was performed.

Each of the optical disc A and the optical disc B was evaluated in termsof signal properties of pits and signal properties of a shallow U-shapedwobbling groove, using an optical pickup at a laser wavelength of λ=650nm equipped with an objective lens with a numerical aperture of NA=0.65as an evaluation machine. Push-pull signals were used for tracking.

Concerning to the pits, it was confirmed that it was possible to realizethe signal properties of stable tracking and stable reproduction of thesignals supported in the pits in the optical disc A and the optical discB. Moreover, jitters of the optical disc A and the optical disc B wererespectively 6.8% and 6.7%.

Concerning the wobbling groove, the bottoms of the shallow U-shapedwobbling grooves of the optical disc A and the optical disc B wereformed to be wider as shown in the above example, and it was possible toobtain a sufficient amount of the push-pull signals, which reveals thatit was possible to stably reproduce the wobble signals in any groovewith a depth in a range of 19-42 nm in the optical discs A and theoptical discs B. Furthermore, jitters of the optical disc A and theoptical disc B when recording and reproducing of the shallow U-shapedwobbling groove were respectively 7.3-7.8% and 7.1-7.5%, even if thedepth of the wobbling groove was changed.

Thus, it was confirmed that the optical recording media, which has theformat of the pits and the U-shaped wobbling groove shallower than thepits according to the embodiment, were able to realize the stablereproduction of the pit signals, the stable reproduction of the wobblesignals, and the stable recording and reproducing in the wobblinggroove.

Here, an optical disc was manufactured using a master where the pattern80 of a shallow wobbling groove was exposed independently with a thindiameter of a spot only using the 2-1 exposure beam 61 as a comparativeexample, and evaluation thereof was performed. Consequently, the crosssection of the wobbling groove of the master had a shallow V-shaped formand the width of a bottom thereof was almost 0, because the shallowgroove was exposed to single narrow beam. In the optical recordingmedium having the above wobbling groove, the aperture width of thewobbling groove was about 320 nm, but the bottom width was 0 nmsubstantially, so it was impossible to obtain a sufficient amount ofsignals.

In addition, when the depth of the wobbling groove was 30 nm or less, itwas substantially impossible to reproduce the wobble signals. Moreover,when the minimum value of the aperture width of the wobbling groove is290 nm and the bottom width was 50 nm or more under the specifiedconditions of the optical pickup as described above, it was confirmedthat good reproduction of the wobble signals was possible. Based onthis, it is estimated that the bottom width of the wobbling groove ispreferably 50 nm or more, and the ratio of the bottom width to theaperture width is preferably set to 17% or more. Needless to say, thedetails of the wobbling groove were not limited only to this.

In addition, the invention can widely be applied to optical recordingmedia having a format of pits and a wobbling groove with a shallowU-shaped cross section form, and masters which is used for manufacturingthereof. Moreover, any optical recording medium can be in scope ofobjects of the invention, for example, read-only optical recordingmedia, optical recording media that allow data to be rewrittenrepeatedly, or optical recording media that allow data to be writtenonce but not to be erased.

Particularly, there is no limit to data recording processes of theoptical recording media, and any optical recording medium, for example,read-only optical recording media having pre-recorded data,magneto-optical recording media for recording and reproducing data usingmagneto-optic effects or phase-change type optical recording media forrecording and reproducing data using phase change of a recording layer,can be in scope of objects of the invention.

Moreover, in the invention, the beams to be recombined are not limitedonly to two or three ones, and four, five, or more beams can be alignedand arranged by installing more PBS.

Further, the latent image of the wobbling groove having certain bottomwidth can be formed by oscillating single beam in the radius directionof the master at certain oscillation within certain period to form anartificial (apparent) broad spot in the radius direction of the master.

Moreover, it is applicable not only to optical recording methods oroptical recording apparatuses but also to signal recording systems orapparatuses, systems or apparatuses having both the functions, and thelike.

As described above, according to the optical recording medium of theinvention, the groove is formed so that the groove depth is shallowerthan that of the pits and the cross section thereof is U-shaped, whichproduces the effects that sufficient amount of the servo signals or thepush-pull signals can be obtained during the reproduction. Moreover, itis possible to control dispersion in the distribution of the depth ofthe groove, which also produces the effects of securing the uniformrecord reproducing properties.

Moreover, according to the master of the invention, and the apparatusand method for manufacturing the master for manufacturing opticalrecording medium of the invention, the optical deflection for wobblingis performed on the single exposure beam supplied from the light source,the beam is divided into the plural exposure beams after that, theplural exposure beams are arranged to be aligned at certain widths inthe radius direction of the master, the exposure beam with the spotwider in the radius direction of the master than that of the abovesingle exposure beam is irradiated to the master in order to expose thelatent image for forming the groove with the U-shaped cross section onthe master, and the latent image is developed to obtain the masterhaving the original form of the groove with the U-shaped cross section.This produces the effects that the groove of the optical recordingmedium, which is manufactured using the master, is shallow with theU-shaped cross section having the flat bottom with certain width.

Moreover, the optical deflection for wobbling is performed on the singleexposure beam supplied from the light source, the beam is divided intothe plural exposure beams after that, the plural exposure beams arearranged and aligned at certain widths in the radius direction of themaster to form the exposure beam with the wider spot in the radiusdirection of the master. Thus, the shallow wobbling groove having theU-shaped cross section, and the flat bottom with certain width cansurely be formed with ease without producing various disadvantages, forexample, phase shifts of the plural exposure beams, interference duringthe final irradiation of the master, and disordered wobbles due todiffering polarizing conditions for the wobbling in these exposurebeams. And realizing such shallow wobbling groove having the bottom withcertain width can accomplish more improvement in recording density.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

1-10. (canceled)
 11. A method of manufacturing a master formanufacturing optical recording medium where a groove and plural pitsformed and arranged dispersedly in a circumference direction, are formedon a substrate, wherein a single exposure beam supplied from a lightsource is divided into two beams with a first beam splitter, one beam ofthe divided beams is pit-modulated and irradiated to a surface of themaster to form a latent image for forming the pits, the other beam ofthe divided beams is optically deflected for wobbling, and divided intoplural exposure beams with a second beam splitter, and the pluralexposure beams are arranged to be aligned at certain widths in theradius direction of the master with a polarization beam splitter and anexposure beam with a spot wider in the radius direction of the masterthan that of the single exposure beam is irradiated to the surface ofthe master in order to form a latent image for forming the groove withan U-shaped cross section on the surface of the master.
 12. A method formanufacturing a master for manufacturing optical recording medium havingat least a groove on a substrate, wherein a single exposure beamsupplied from a light source is optically deflected for wobbling anddivided into plural exposure beams with a beam splitter, the pluralexposure beams are arranged to be aligned at certain widths in theradius direction of the master with a polarization beam splitter, and anexposure beam with a spot wider in the radius direction of the masterthan that of the above single exposure beam is irradiated to a surfaceof the master in order to form a latent image for forming the groovewith an U-shaped cross section on the surface of the master.
 13. Amethod for manufacturing a master for manufacturing optical recordingmedium according to claim 12, wherein the groove is a wobbling groovewhich is formed to have a wobbled tracking.
 14. A method formanufacturing a master for manufacturing optical recording mediumaccording to claim 12, wherein the groove has a ratio of a bottom widthto a aperture width in the U-shaped groove to be set to 17% or more.